Universal trailer for a longwall roof support for longwall underground mining

ABSTRACT

A universal trailer for transporting a variety of longwall roof supports for a longwall underground mine is disclosed, along with a method of using such a trailer. The trailer includes a wheeled, U-shaped frame that can be raised and lowered relative to the ground to lift and off-load a roof support. The trailer includes forward and rearward supports, either of which may be shiftable.

RELATED APPLICATIONS

[0001] This application claims domestic priority from U.S. Provisional Application Ser. No. 60/347,725, filed Jan. 10, 2002, and from U.S. Provisional Application Ser. No. 60/391,696, filed Jun. 26, 2002.

FIELD OF THE DISCLOSURE

[0002] This disclosure relates generally to mining, and, more particularly, to a universal trailer for supporting and/or transporting a longwall roof support of the type conventionally used used in longwall underground mining.

BACKGROUND

[0003] Longwall mining is an underground coal mining technique. An exemplary longwall mining operation is illustrated in FIGS. 1A and 1B. As shown therein, two parallel access roads are created into the coal seam. The access roads are used to provide access to the longwall being mined, to transport mined coal away from the longwall, and to provide ventilation.

[0004] A crosscut tunnel is formed through the coal seam at approximately 90° to the access roads. A side of the crosscut tunnel to be mined is referred to as the longwall, and a longwall mining machine is positioned adjacent the longwall so as to be moveable back and forth along the face of the longwall during the miningoperation. As is known, the longwall mining machine shears cola from the face of the longwall. The sheared coal falls onto a conveyor belt which transports the coal to the access roads for transport to the surface.

[0005] The roof supports are self-advancing such that, as the longwall is mined and the longwall mining machine advances toward the receding longwall, the roof supports likewise move forward. As the roof supports advance with the mining machine, the roof of the mine behind the roof supports (i.e., on the side of the supports opposite the longwall being mined) collapses. The collapsed roof is commonly referred to as “goaf.”

[0006] To move the roof supports to a desired location in a mine shaft, one prior art system employed a prime mover pulling a trailer via a hitch connection. These prior art trailers include a wheeled floor, a winch and cable, and, on some units, a hydraulic cylinder. The winch is used to pull a support onto the floor of the trailer for transport. The cylinder, where fitted, may be used to push the support off of the trailer when the desired location is reached. The winch and cylinder, where fitted, must be heavily sized as the weight of a roof support can approach 50 tons.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a perspective view of a trailer constructed in accordance with the teachings of a first discloased example of the invention for carrying a roof support.

[0008]FIG. 1A is a schematic view in perspective of an exemplary longwall mining system.

[0009]FIG. 1B is a perspective view of an exemplary coal shearing mining machine and exemplary roof supports shown in a working position.

[0010]FIG. 2 is a schematic illustration of an exemplary roof support.

[0011]FIG. 3 is a top view of the trailer of FIG. 1 shown in position to carry a roof support (the roof support is shown in dotted lines).

[0012]FIG. 4 is a side view of the trailer and roof support of FIG. 3.

[0013]FIG. 5 is an end view of the trailer and roof support of FIGS. 3-4.

[0014]FIG. 6 is a side view of an example universal trailer constructed in accordance with the teachings of the invention for carrying a Moranbah N roof support (shown in dotted lines).

[0015]FIG. 7 is a side view of the trailer of FIG. 6 carrying a Dartbrook Panzer roof support (shown in dotted lines).

[0016]FIG. 8 is a top view of the trailer of FIGS. 6 and 7 and further showing the outline of the Moranbah N and Dartbrook Panzer roof supports in dotted lines;

[0017]FIG. 9 is a side view of the trailer of FIGS. 6-8 being transported by a load haul dump prime mover.

[0018]FIG. 10 is a rear view showing a rear side hook in more detail.

[0019]FIG. 11 is a top view of the trailer and prime mover of FIG. 10.

[0020]FIG. 12 is a view similar to FIG. 11 but illustrating the turning radius of the trailer/prime mover combination.

[0021]FIG. 13 is a top view of the prime mover of FIG. 11 carrying a fork.

[0022]FIG. 14 is a side view of the prime mover and fork of FIG. 13.

[0023]FIG. 15 is a top view of the prime mover carrying a bucket.

[0024]FIG. 16 is a side view of the prime mover and bucket.

DESCRIPTION OF THE PREFERRED EXAMPLES

[0025] Referring now to FIGS. 1A and 1B, a number of roof supports 8 are positioned along the length of a longwall being mined. As used throughout this description, the term “forward” is used to indicate that portion of the roof support 8 that faces the long wall of the mine when the roof support 8 is in place, while the term “rearward” is used to indicate that portion of the roof support 8 that faces away from the long wall to be mined (i.e., toward the collapsed roof or goaf). Also, although the exemplary forms of the invention described herein are particularly well suited for use in connection with longwall coal mining operations, persons of ordinary skill in the art will readily appreciate that the teachings of the invention are in no way limited to a particular type of underground mining operation.

[0026] A schematic illustration of an exemplary roof support 8 is shown in FIG. 2. As shown in FIG. 2, the typical roof support 8 includes a base 10, a canopy 12 pivoted to the base 10, and hydraulic cylinders 14 for lifting and supporting the canopy 12 relative to the base 10. The roof support includes a forward end 13 and a rearward end 15. In use, the roof support 8 is positioned at a desired location adjacent a wall to be mined (FIG. 1A). The hydraulic cylinders 14 are then actuated to lift the canopy 12 to a support position (shown in FIG. 1B) adjacent, and possibly in contact with, the ceiling of the mine shaft. Typically, a large number of roof supports 8 are positioned side-by-side along the wall being mined as shown in FIGS. 1A and 1B to support the mine ceiling and create a safe cavity.

[0027] A trailer 20 constructed in accordance with the teachings of a first preferred embodiment of the invention for transporting the roof support 8 in an underground mining operation is shown in FIGS. 1 and 3-5. For ease of reference, throughout this description the positional terms “forward” and “rearward” will be used to refer to that portion of the trailer 20 that is disposed toward the front 13 and the rear 15, respectively, of the roof support 8 when the trailer 20 is in the use position adjacent the roof support 8 as shown, for example, in FIGS. 3 and 4. The trailer 20 includes a front end 21 and a rearward end 23.

[0028] For the purpose of selectively underlying a roof support 8, the trailer 20 is provided with a U-shaped frame 22. The U-shaped frame 22 includes two side beams 24 of substantially the same length and a cross-member 26 (see FIG. 4) extending generally between the two side beams 24. Preferably, a hitch 28 is mounted to the cross-member 26 or to any ther suitable portion of the frame 22 in order to provide a means for securing the trailer to a prime mover (for example, the prime mover 29 shown in FIGS. 9 and 11-16) for transport.

[0029] To provide for rolling movement of the trailer 20, a pair of wheels 30 are rotatably mounted to the frame 22. As shown in FIGS. 3-4, each of the wheels 30 is journaled on a support plate 34. Each of the support plates 34 is in turn pivotably mounted to the frame 24 via a pivot pin 36 (see FIGS. 1 and 4) or other suitable arrangement. A second pivot pin 38 couples each of the plates 34 to a first end of a hydraulic cylinder 40. The opposite end of each cylinder 40 is pivotally mounted to the cross-member 26 of the frame 22 via a stanchion 43 (see FIGS. 1 and 4) using a pivot pin 53 a or other suitable arrangement. This construction is such that extending the cylinders 40 will lower the wheels 30 relative to the frame (by pivoting the plate 34 in a generally clockwise direction about the pivot 36 when viewing FIGS. 1 and 4), thus raising the frame 22 away from the ground or other support surface. On the other hand, retracting the cylinders 40 will pivot the plate 34 in a generally counter-clockwise direction about the pivot 36 when viewing FIGS. 1 and 4), thus lowering the frame 22 toward from the ground. Preferably, the hydraulic cylinders 40 are plumbed so that the cylinders 40 operate in synchronism and the frame 22 is, thus, raised/lowered evenly.

[0030] The ability to raise and lower the U-shaped frame 22 permits the trailer 20 to be lowered and then driven under a roof support 8 while the roof support 8 stands on the ground. Raising the frame 22 will then lift the roof support 8 off of the ground for transport.

[0031] To support a longwall roof support 8 on the frame 22 during lifting, lowering and/or transport, the trailer 20 is further provided with shiftable support arms 41. As shown in FIGS. 1, 3 and 4, each of the support arms 41 is preferably pivotably mounted to a free or rearward end 43 of a respective one of the side beams 24. Preferably, the support arms 41 are mounted to their respective side beams 24 via a vertical pin 45 such that each of the support arms 41 can be pivoted in the plane of the U-shaped frame 22. To this end, an extension lug 42 extends from each of the support arms 41. Each of these lugs 42 is pivotably coupled to an end of a hydraulic cylinder 44 by a pivot 47. The other end of the hydraulic cylinder 44 is mounted to the appropriate side beam 24 using another pivot 49. In the disclosed example, the pivot pin 45 extends between a pair of spaced apart plates 51 (FIGS. 1 and 5) mounted to the frame 22 generally toward the rear end 23 of the trailer 20. The side beams 24 cooperate to generally define a space or opening 53 (FIGS. 1 and 3) between the side beams 24. Extending and/or retracting the cylinders 44 will pivot their respective support arms 41 generally horizontally through approximately 90° . Thus, in a first position, each of the support arms 41 is positioned in substantial alignment with its respective side beam 24 (i.e., disposed so as to generally not extend into the opening 53) to facilitate driving under an/or pulling away from a roof support 8. In a second position, each of the support arms 41 is pivoted inward from its first position (e.g., at approximately 90° from its respective side beam 24 so as to generally extend into the opening 53) to thereby underlie and support the roof support 8 when lifting, lowering and/or transporting the roof support 8. Alternatively, the support arms 41 may be linearly extendable and retractable, may pivot about a horizontal or angled axis, or may shift between an extended/engaged position and a retracted/disengaged position along an arcuate or non-linear path.

[0032] The support arms 41 provide two contact or support points for supporting the rear end 23 of the longwall roof support 8 on the trailer 20. To provide a further contact point toward the opposite or forward end 21 of the trailer 20, the trailer 20 is further provided with a movable cross-beam 50. As shown in FIGS. 1 and 4, the cross-beam 50 is mounted to a pair of arms 52 which is, in turn, are pivotably coupled to a pair of stanchions 54. The stanchions 54 are mounted to the cross-member 26 of the frame 22, or to any other suitable portion of the frame 22.

[0033] The movable cross-beam 50 includes an extension 58 as shown in FIG. 4. This extension 58 is pivoted to an end of a hydraulic cylinder 60. The opposite end of the cylinder 60 is pivotably mounted to the cross-member 26 (see FIG. 4). Extending/retracting the cylinder 60 will raise/lower the cross-beam 50 to engage and assist in lifting and/or supporting the roof support 8 as shown in FIG. 4.

[0034] If desired, the movable cross-beam 50 can be replaced with a fixed cross-beam (not shown). When used, the fixed cross-beam is preferably securely mounted to the frame 22 and operates to assist in supporting and/or lifting the roof support 8.

[0035] In operation, when it is desired to pick up a roof support 8, the trailer 20 is hitched to a prime mover and transported to a position adjacent the roof support 8. The frame 22 is lowered relative to the wheels 30 and the support arms 41 are positioned in alignment with the side beams 24. The trailer 22 is then moved under the roof support 8 with the side beams 24 generally straddling the roof support 8. The support arms 41 are then pivoted inward as explained above such that they extend into the opening 53 so as to be positioned below a portion of the roof support 8. The frame 22 is then raised off the ground by extending the cylinders 40 so as to pivot the support plates 34 about the pivot 36. This raises the frame 22 relative to the ground, and in so doing brings the trailer 20 into contact with the roof support 8 from below so as to to lift the roof support 8 from the ground. If employed, the movable cross-beam 50 is raised to assist in supporting and/or lifting the roof support 8, preferably before the trailer 22 is raised.

[0036] When the roof support 8 is lifted as explained above, the prime mover can move the trailer 20 and roof support 8 to the desired location. The above procedure is then reversed to lower the roof support 8 to the ground and move the trailer 20 away from the roof support 8.

[0037] Because roof supports are typically very heavy (e.g., 40-50 tons), persons of ordinary skill in the art will appreciate that the trailer 20 should be constructed of suitable materials having strength and stiffness properties adequate to carry the appropriate loads. In the illustrated example, the trailer components are constructed of steel (e.g., the side beams 24 are solid, 4-inch plates of steel). The sizing of the appropriate components would be well within the art of those of ordinary skill in the art of steel design.

[0038] The tires 30 should also be suitably selected to handle heavy loads (e.g., 24-inch hard rubber tires could optionally be used in this role). Preferably, the wheels 30 of the trailer 20 are equipped with brakes. Although any type of brake could be used in this role, in the illustrated trailer 20, oil enclosed, disk-type brakes are employed.

[0039] Referring now to FIGS. 6-10, a universal trailer 120 constructed in accordance with the teachings of a second disclosed example of the present invention for transporting a roof support in an underground mining operation is shown.

[0040] For the purpose of selectively underlying a roof support, the trailer 120 is provided with a U-shaped frame 122. The U-shaped frame 122 includes two side beams 124 of substantially the same length and a cross-member 126 (see FIG. 8) joining the two side beams 124. A hitch 128 is mounted to the cross-member 126 to provide a means for securing the trailer to a prime mover 129 for transport.

[0041] To provide for rolling movement of the frame 122, wheels 130 are rotatably mounted to the frame 122. As shown in FIGS. 6-8, each of the wheels 130 is journaled on a support plate 134. Each of the support plates 134 is in turn pivotably mounted to the frame 124 via a pivot pin 136. A second pivot pin 138 couples each of the plates 134 to a first end of a hydraulic cylinder 140. The opposite end of each cylinder 140 is pivoted to the cross-member 126 of the frame 122 via a stanchion 143. In the disclosed example, this construction allows the frame to be raised/lowered relative to the wheels 130 by extending/retracting the cylinders 140. Preferably, the hydraulic cylinders 140 are plumbed so that the cylinders 140 operate in synchronism and the frame 122 is, thus, raised/lowered evenly.

[0042] The ability to raise and lower the U-shaped frame 122 permits the trailer 120 to be lowered and then driven under a roof support 8 while the roof support 8 stands on the ground. Raising the frame 122 will then lift the roof support 8 off of the ground for transport.

[0043] To support a longwall roof support 8 on the frame 122 during lifting, lowering and/or transport, the trailer 120 is further provided with two forward hooks 139 and two rear support arms 141. As shown in FIG. 4, the forward hooks 139 are rigidly suspended from the cross-bar 26. In the illustrated example, the two rigid hooks 139 are spaced inwardly from the side beams 124, extend toward the rear of the trailer 120, and are spaced symmetrically about the longitudinal center axis of the trailer. As shown in FIGS. 6, 7 and 9, the tips of the hooks 139 are suspended at a slightly lower height than the bottom edge 124 a of the side beam 124.

[0044] As also shown in FIG. 6, each of the rear support arms 141 is preferably pivotably mounted to the free end of a respective one of the side beams 124. More specifically, in the illustrated example, each of the rear support arms 141 has an L-shaped cross-section. The top part of each arm 141 is respectively journaled for pivoting movement between two, vertically oriented, angle plates 142. As shown in FIGS. 8, 10 and 11, each pair of angle plates 142 is mounted to a platform 144. Each of the platforms 144 is mounted to, and terminates, a respective one of the side beams 124 (FIG. 11). As shown in FIGS. 8 and 10, the bottom portions of the L-shaped support arms 141 are inwardly directed toward the center, longitudinal axis of the trailer.

[0045] A hydraulic cylinder 145 is mounted to each of the platforms 144 between the angle plates 142. The cylinders 145 are pivotally mounted to the back of their respective rear support arms 141 as shown in FIG. 10. Thus, extending the cylinder 145, pivots the rear support arms 141 inwardly. In a first position, each of the support arms 41 is positioned in a substantially vertical plane (e.g., the position shown in dotted lines in FIG. 10) to facilitate driving the trailer under and/or pulling the trailer away from a roof support 8. In a second position (e.g., the position shown in solid lines in FIG. 10), each of the support arms 141 is pivoted inward from its first position and into the cavity 153 defined between the side beams 124 to thereby underlie and support the roof support 8 when lifting, lowering and/or transporting the roof support 8. Because the support arm 8 can be pivoted to any of a number of inward positions permitted by the extension length of the cylinders 145, the rear support arm 8 can accommodate a range of roof support widths.

[0046] The support arms 141 provide two contact points for supporting a longwall roof support 8 on the trailer 120. The forward hooks 139 provide two more contact points at the opposite end of the trailer 120 for supporting the roof support 8.

[0047] In operation, when it is desired to pick up a roof support 8, either one of the disclosed exemplary trailers 20, 120 may be hitched to a prime mover 29 (FIGS. 9 and 11-16) and transported to a desired position adjacent the roof support 8. The hitch 28 is lowered by the prime mover 29 as explained below, and frame 22 is lowered relative to the wheels 130 such that the forward hooks 139 penetrate the soft floor surface. The prime mover 29 then forces the trailer 120 rearwardly relative to the stationary roof support 8 until the forward hooks 139 are positioned under the forward end 121 of the base 110 of the roof support 8 (see FIGS. 6 and 8). The rear side hooks 141 are then pivoted inward as explained above to forcibly insert the arms 141 beneath the rear sides of the chock base. The hitch 128 and frame 122 are then raised to lift the roof support 8 from the ground.

[0048] When the roof support 8 is lifted as explained above, the prime mover 29 can move the trailer 120 and roof support 8 to a desired location. The above procedure is then reversed to lower the roof support 8 to the ground and move the trailer 120 away from the roof support 8.

[0049] Again, the tires 130 should be suitably selected to handle heavy loads (e.g., 24-inch hard rubber tires could optionally be used in this role), and the trailer wheels 130 may be equipped with brakes, such as oil enclosed, disk-type brakes.

[0050] Because the rear support arms 141 can accommodate roof supports 8 of different widths, the trailers 20 and/or 120 may be termed “universal” in the sense that the trailers can be used to transport different types of roof supports 8. For example, as shown in FIGS. 6 and 8, the illustrated trailer 120 can be used to transport a Moranbah N roof support as well as a Dartbrook Panzer roof support.

[0051] Persons of ordinary skill in the art will readily appreciate that any type of prime mover can be used to transport the trailers 20, 120. In the illustrated example, the prime mover 29 is implemented by a load haul and dump (LHD) prime mover 29 (see FIG. 9). As shown in FIG. 11, the LHD prime mover 29 has an articulated body. More specifically, it includes a rear chassis 250 and a forward chassis 252. The rear chassis 250 includes two wheels 254 and a hitch 256. The hitch 256 is structured to releasably secure the hitch 28 of the trailer 20 or 120. The hitch 256 can be raised and lowered by the LHD prime mover 29 to raise/lower the hitch 28 and, thus, the forward end of the trailer 20.

[0052] The forward chassis 252 also includes two wheels 258. The engine 260 is carried by the forward chassis 252. A control cab 262 is also mounted on the forward chassis 252 for controlling operation of the LHD 29. The rear chassis 250 and forward chassis 252 are coupled at upper and lower pivot points 264 (see FIG. 12) to provide articulation therebetween. As shown in FIG. 12, the articulated prime mover 29 and trailer 20 or 120 are highly maneuverable to facilitate movement through narrow turns in mine tunnels.

[0053] The illustrated prime mover 29 is a versatile machine. In addition to its function of moving and operating the trailer 120 (the trailer 120 can preferably be raised and lowered remotely via the support plates 134 and the hitch 28 by an operator in the cab 262 of the prime mover 29 via conventional electrical signal controls in that the frame can be lowered relative to the wheels and/or the hitch itself can be lowered), the prime mover 29 can also be equipped with a fork 70 (see FIGS. 13-14) and/or a bucket 72 (see FIGS. 15-16) for use in various lifting, digging, and/or loading operations. To this end, the rear chassis 250 is provided with a plurality of hydraulic cylinders 276 and a universal yoke 278. By extending/retracting the cylinders in various combinations, the yoke 278 and any implement attached thereto (e.g., hitch 56, fork 270, bucket 272, etc.) can be raised/lowered in a conventional fashion.

[0054] As shown in FIGS. 9, 14 and 16, the universal yoke 278 includes two pins 280. By aligning bores in the yoke 278 and bores in the implement of choice and inserting the pins 280 through the aligned bores, the implement of choice is removably secured to the yoke 278.

[0055] Although certain apparatus constructed in accordance with the teachings of the invention have been described herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all embodiments of the teachings of the invention fairly falling within the scope of the appended claims either literally or under the doctrine of equivalents. 

What is claimed:
 1. A trailer for transporting an underground mining roof support over a support surface, the trailer comprising: a U-shaped frame having a forward portion and a pair of rearwardly extending side beams; a pair of wheel supports, each of the wheel supports shiftably mounted to the frame and shiftable between a first position in which the frame is disposed adjacent the support surface and a second position in which the frame is raised away from the support surface; at least one actuator mounted to the frame and operatively engaging the wheel supports, the at least one actuator being operable to shift the wheel supports between the first and second positions; a forward support disposed generally adjacent to the forward portion of the frame, the forward support adapted to engage a first portion of the roof support; and a pair of shiftable rear supports, each rear support carried by a corresponding one of the rearwardly extending side beams, each rear support adapted to engage a second portion of the roof support, each rear support including an actuator operable to shift the rear support between a first position and a second position.
 2. The device of claim 1, wherein the rearwardly extending side beams are spaced apart to define an opening, and wherein each rear support extends into the opening when the rear support is shifted toward the second position.
 3. The device of claim 2, wherein each rear support is pivotable about a generally vertical axis.
 4. The device of claim 2, wherein each rear support is pivotable about a generally horizontal axis.
 5. The device of claim 1, wherein the frame includes a cross-member disposed adjacent the forward portion of the frame and extending between the side beams, and wherein the forward support is carried by the cross-member.
 6. The device of claim 5, wherein the forward support includes a pair of hooks depending from the cross-member.
 7. The device of claim 6, wherein each hook faces rearward.
 8. The device of claim 7, wherein each hook is sized and shaped to be driven into the support surface in response to rearward movement of the trailer when the wheel supports are in the first position.
 9. The device of claim 7, wherein each of the side beams includes a bottom edge, and wherein a lower portion of each hook extends below the bottom edge of each side beam.
 10. The device of claim 1, wherein the forward support is defined at least in part by a cross-beam mounted adjacent the forward portion of the frame.
 11. The device of claim 10, wherein the cross-beam is shiftable relative to the frame between a raised position and a lowered position, and including at least one actuator operatively connecting the the cross-beam and the frame and operable to shift the cross-beam between the raised and lowered positions.
 12. The device of claim 10, wherein the cross-beam is pivotally mounted to the frame.
 13. The device of claim 12, wherein the cross-beam includes a pair of spaced apart arms, and wherein each of the arms is pivotally mounted to a stanchion.
 14. The device of claim 1, including a pair of actuators mounted to the frame, each actuator operatively engaging a corresponding one of the wheel supports, the actuators being synchronized and further being operable to shift the wheel supports between the first and second positions.
 15. The device of claim 1, wherein each of the wheel supports is pivotally mounted to the frame.
 16. The device of claim 15, wherein each of the wheel supports includes a plate, each plate rotatably supporting a wheel, each plate pivotally connected to the frame and operatively connected to the actuator.
 17. A trailer for transporting an underground mining roof support over a support surface, the trailer comprising: a U-shaped frame having a forward portion and a pair of rearwardly extending side beams; a pair of wheel supports, each of the wheel supports rotatably supporting a wheel, each of the wheel supports shiftably mounted to the frame and moveable between a first position and a second position; actuation means mounted to the frame and operatively engaging the wheel supports, the actuation means operable to shift the wheel supports between the first and second positions to thereby alter the position of the frame relative to the support surface; a forward support, the forward support positioned on the frame to engage a forward portion of the roof support when the trailer is positioned adjacent the roof support; and a pair of rear supports, each rear support carried by a corresponding one of the rearwardly extending side beams, each rear support positioned on the frame to engage a rearward portion of the roof support when the trailer is positioned adjacent the roof support.
 18. The device of claim 17, wherein each of the rear supports is shiftable between an extended position and a retracted position, and including an actuator for shifting each of the rear supports between the extended and retracted positions.
 19. The device of claim 18, wherein the rearwardly extending side beams are spaced apart to define an opening, and wherein the rear supports extend toward the opening when the rear supports are shifted toward the extended position.
 20. The device of claim 18, wherein the rear supports are pivotable about a generally vertical axis.
 21. The device of claim 18, wherein the rear supports are pivotable about a generally horizontal axis.
 22. The device of claim 17, wherein the frame includes a cross-member disposed adjacent the forward portion of the frame, and wherein the forward support is carried by the cross-member.
 23. The device of claim 17, wherein the forward support extends downwardly from the frame.
 24. The device of claim 17, wherein the forward support comprises at least one rearward facing hook.
 25. The device of claim 24, wherein a lower portionof the frame is disposed on the support surface when the wheel supports are in the first position, and wherein the hook depends downwardly from the frame, the hook sized and shaped to be driven into the support surface in response to rearward movement of the trailer when the wheel supports are in the first position.
 26. The device of claim 17, wherein the forward support is defined at least in part by a shiftable cross-beam mounted adjacent the forward portion of the frame, the cross-beam including an actuator and being shiftable relative to the frame between a raised position and a lowered position.
 27. The device of claim 26, wherein the cross-beam includes a pair of spaced apart arms, and wherein each of the arms is pivotally mounted to a stanchion.
 28. The device of claim 17, wherein each of the wheel supports includes a plate pivotally connected to the frame and operatively connected to the actuation means.
 29. A trailer for transporting an underground mining roof support over a support surface, the trailer comprising: a U-shaped frame having a forward portion and a pair of rearwardly extending side beams; a pair of wheel supports, each of the wheel supports rotatably supporting a wheel, each of the wheel supports shiftably mounted to the frame and moveable between a first position and a second position; actuation means mounted to the frame and operatively engaging the wheel supports, the actuation means operable to shift the wheel supports between the first and second positions to thereby alter the position of the frame relative to the support surface; a forward support, the forward support positioned on the frame to engage a forward portion of the roof support when the trailer is positioned adjacent the roof support; a pair of rear supports, each rear support carried by a corresponding one of the rearwardly extending side beams, each rear support positioned on the frame to engage a rearward portion of the roof support when the trailer is positioned adjacent the roof support; atleast one of the forward support and rear supports shiftable relative to the frame.
 30. A method of using a prime mover to transport an underground mining roof support over a support surface, the method comprising the steps of: providing a trailer having a frame adapted to straddle at least a portion of the roof support, the frame including a forward support, at least one rear support, and a pair of shiftable wheel supports, each of the wheel supports rotatably supporting a wheel and shiftable relative to the frame between a first position and a second position; shifting a lower portion of the frame toward the support surface by shifting the wheel supports to the first position; positioning the trailer adjacent the roof support with the forward support adjacent a first part of the roof support and with the rear support adjacent a second part of the roof support; shifting the wheel supports toward the second position to thereby lift at least one of the first and second parts of the roof support off the support surface, whereby the trailer and the roof support can be moved by a prime mover.
 31. The method of claim 30, wherein the rear supports are shiftable between an extended position and a retracted position, and including the additional steps of: shifting the rear supports toward the retracted position prior to positioning the trailer adjacent the roof support; and shifting the rear supports to the extended position after positioning the trailer adjacent the roof support.
 32. The method of claim 30, wherein the front support comprises a hook, and including the step of driving the hook under the front part of the roof support by moving the trailer rearward with respect to the roof support. 